Tuning control system for signal seeking receivers



June '14, 1949.

M. G- NICHOLSON, JR

TUNING CONTROL SYSTEM FOR SIGNAL SEEKING RECEIVERS Filed Oct. 4, 1944 ATTORNEY Patented June 14, 1949 UNITED STATES PATENT OFFlCE TUNING CONTROL SYSTEM FOR SIGNAL SEEKING RECEIVERS Madison G. Nicholson, Jr., Snyder, N. Y., assignor to ColonialRadio Corporation, Buffalo, N. Y.

Application October 4, 1944, Serial No. 557,192

11 Claims. V

This invention relates to a tuning control system for signal seeking receivers. In signal seeking receivers", as is well known, there is provided a motor for operating the tuning or signal selecting instrumentality;

When such a receiver is placed inoperation, the motor begins to operate and the tuning circuits scan the frequency range over which the receiver is arranged to operate. When a signal of predetermined strength is tuned in, a relay operates, opening the motor circuit and stopping thetuning instrumentality in position where the signal is received.

Under certain conditions noise or static impulses may'causethe relay to operate, stopping the motor circuit in response to static or noise. This operation is, of course, undesired, and various arrangements have been devised and used to distinguish between desired signals on which the tuning should stop, and static or noise on which it should not stop;

In accordance with this invention, I provide a new and improved means for stopping the tuning instrumentality inresponse to desired signals, which means is relativelyinsensitiveto static or noise.

In accordance with the principles of my invention- I may employ for the purpose of stopping the tuner motor a circuit of the frequency discriminator rectifier type operated by the signal after the-signal frequency has been changed by the action of the converter. The new frequency changes, of course, as the oscillator frequency is varied, aswill be understood. As is well known, this-hasa frequency vs. output characteristic resembling an Sl'ying on its side.

As the tuning instrumentality is varied, the frequency of the signal approaches the frequency to which the discriminator istuned, the voltage out-put of the frequency discriminator-rectifier network rises to a positive peak. Continued variation of tuning in the same direction then causes a substantially linear decrease of output through zero and to a negative peak of approximately the same value as the positive peak, and still further variation of tuning in the same direction causes a continued reduction in output. In other words, as an incoming signal(converted to intermediate frequency) is tuned across the discriminator' spectrum, the signal acts, in the frequency discriminator-rectifier circuit, as if it were frequency modulated.

I employ the positivepeak when the signal is approaching to cause the operation of therelay to stop the 'tunermotor, and also to provide a To provide a signal seeking receiver in which false stoppages of the tuner motor from noise or static impulses are greatly reduced or substantially eliminated.

To provide a signal seeking receiver utilizing a discriminator type circuit for controlling the operation of the tuner motor.

To provide a signal seeking receiver in which a discriminator type circuit is employed to distinguish between desired signals and noise or static.

To provide a receiver of the class described employing a discriminator circuit to control the tuner motor, the circuit operating in such a manner that the motor will be stopped when an incoming signal of predetermined strength is received but false stoppages from static or noise impulses are substantially eliminated or greatly reduced.

Still other objects and advantages of my invention will be apparent from the specification.

The features of novelty which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its fundamental principles and as to its particular embodiments, will best be understood by reference to the specification and accompanying drawing, in which:

The single figure is acircuit diagram of asignal seeking receiver in accordance with my invention.

In a receiver of the superheterodyne type, as will be understood, the interaction or beat between incoming signals and the local oscillator produces new signals, one having a carrier frequency which is the difference between the incoming signal and the local oscillator frequencies, and the other the sum, and one of these new frequencies will pass through the intermediate frequency amplifier only when its frequency corresponds to that to which the I. F. channel is tuned.

Viewed from the input of the discriminator, which may be supplied from the output of the I. F. amplifier, tuning through an incoming signal gives a frequency modulation type of frequency variation in the discriminator and this is especially true if the output of the I. F. amplifier, before being applied to the discriminator, is passed through a limiting amplifier so as to substantially eliminate variations of amplitude.

As the oscillator tunes through an incoming signal, the discriminator will deliver a voltage output which rises to a positive peak, then decreases linearly to a substantially equal negative peak, and then returns to zero. I utilize this action to control the tuning motor in a manner which will be more fully described with reference to the figure of the drawing.

In this figure, I represents an antenna supplying signal voltage to the converter or first detector 2, which may be tuned by a suitable tuning instrumentality herein diagrammatically represented as variable condenser 3, but which may be any other suitable tuning instrumentality, such as a variable inductance or permeability tuner.

Local oscillator 4 may also be provided, tuned by a variable tuning instrumentality, such as variable condenser 5 or other tuner, and these tuning instrumentalities may be ganged together and driven by motor 33 through a mechanical connection 34. The oscillator 4, while separately indicated, may be a part of converter 2 if desired, and this may be accomplished by utilizing a pentagrid converter tube, as will be understood by those skilled in the art.

The output of converter 2 may then be passed through intermediate frequency amplifier 6 and through detector and audio amplifier I, and may operate a suitable indicating instrument, such as load speaker 8.

Since the elements so far described are well understood, their arrangement is not described in detail.

In accordance with my invention, I withdraw from the output of the intermediate frequency amplifier 6 a portion of the incoming signal, and this may be impressed through condenser 9 and resistance Ill upon the control circuit of limiting amplifier ll. This limiter may, however, be omitted if desired, although the provision of the limiter does provide a definite improvement in operation. In the embodiment of the invention herein described this is a tube of the pentode type, having cathode 0, control electrode H91. screen llgz, suppressor g3, and anode Ila.

The cathode is connected to ground, control electrode I I or is connected to the high side of resistor l0, screen electrode is connected to +B through resistance 23 which is by-passed to ground through fixed condenser 12, and suppressor grid N93 is connected to the cathode. Anode Ila is connected to +3 through primary coil [3 of the discriminator transformer shunted by variable condenser M. The anode side of winding it is connected through fixed condenser to the midpoint of coil l6, which is shunted by fixed condenser l1, and the terminals of coil it are connected to anodes 18a and 19a of diodes l8 and i9 respestively.

Cathode I80 is connected to ground, and cathode 290 is connected to ground through resistors 20 and 2| shunted by condenser 22 and through resistance 24 to control electrode 25g of control tube 25. The midpoint of coil 5 is connected to ground through resistance 2|.

Tube 25 may, and preferably will, be a tube of the thyratron type having cathode 250, control electrode 259 and anode 25a. Cathode 250 is connected to ground through resistance 26 and the anode through the actuating coil 28 of the relay to +3. The cathode is connected to +3 through resistance 2?.

The relay has armature 29,.back contact 38, and front contact 3 l, and is spring biased to back contact 38, in which position it closes the circuit from suitable current source 32 through motor 33 driving the tuning instrumentalities.

Push button switch 35 is provided for opening the plate circuit of tube 25. This push button switch is spring biased to closed position, but when momentarily depressed by the operator, opens the plate circuit to tube 25, interrupting the current therein, which in turn permits armature 29 to close by spring bias against back contact 38, thereby starting the tuning motor in operation.

The operation of the circuit will now be described. Assuming that the on and off switch (not shown) has been turned on so that the tubes are heated up, the operator will momentarily press switch 35, opening the plate circuit of tube 25 and deionizing it if by any chance it has been ionized.

Armature 29 will close against contact 35, starting tuning motor 33, and the tuning of converter 2 and oscillator 4 will now vary. If these tune across a signal, a portion of the output of I. F. amplifier 6 will be impressed upon limiter i l and thence upon the discriminator D, and the output of the discriminator will rise toward its positive peak.

The plate voltage and bias of tube 25 are preferably So chosen that as this positive peak is approached, the bias on tube 25 is overcome and the tube will ionize and will remain ionized until switch 35 is again opened. The current through relay winding 28 will greatly increase, and armature 29 will be drawn to front contact 3|, thus opening the motor circuit and stopping the variation of the tuner.

It will be apparent that armature 29 will not open at contact 30 instantaneously, since the faster operating relays require approximately one millisecond to function, and, also, since motor 33 and its associated parts have some inertia, they will continue to operate for a small interval of time even after the motor circuit has been opened.

However, for any particular receiver, this amount of overrun is substantially constant, and it may be chosen of the right value so that although the motor circuit is opened at or near the positive peak of the discriminator output, the inevitable time delay and coasting, which occurs before the system comes to rest, will carry the tuning to or near the zero point between the two peaks of the discriminator, and thus the tuning will be very exact.

The discriminator D is balanced for impulses having substantially uniform energy distribution over the I. F. spectrum and, therefore, is substantially unresponsive to noise and static. Moreover, they are limited by limiter H to a predetermined value and again reduced in amplitude by the sharp tuning of the discriminator, which is preferably tuned to a band width which is a small fraction, say 1 6 of the Width of the I. F. band, so that the bias on tube 25 may be readily adjusted at such a value that the voltage produced by them is not sufiicient to overcome the bias of tube 25, and, accordingly, they will not 5.1 cause ionization of the tube with consequent stoppage of tuning.

In the operation of the system as appliedtoa superheterodyne, the discriminator will'be tuned to have its intermediate frequency occur at the intermediate frequency of the receiver and will remain in that position.

While I have shown and described a certain preferred embodiment of my invention, it will be understood that modifications and changes may be made without departing-from the spirit and scope thereof, as will be clear to those skilled in the art.

In this application I have explainedthe principles of my invention and the best mode in which I have contemplated applying those principles, so as to distinguish my invention from other inventions; and I have particularly'pointed out and distinctly claimed the part, improvement, or combination which I claim as my invention or discovery.

I claim:

1. In a signal seeking receiver, in combination, signal circuit tuning means, electrical power means for varying said signal circuit tuning means, a normally closed switch controlling said power means, and means for opening said switch to ole-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a balanced type of frequency discriminator-rectifier supplied by incoming signals, and a control tube responsive to the output of said frequency discriminator-rectifier as the incoming signal frequency enters the frequency response spectrum of the frequency discriminator-rectifier, for effecting said opening of said switch to deenergize the electric power means.

2. In a signal seeking receiver, in combination, signal circuit tuning means, electrical power means for varying said signal circuit tuning means, a normally closed switch controlling said power means, and means for opening said switch to de-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a signal amplitude limiter actuated by incoming signals, a balanced type of frequency discriminator-rectifier supplied by the output of said limiter, and a control tube responsive to the output of said frequency discriminator-rectifier as the incoming signal frequency enters the frequency response spectrum of the frequency discriminator-rectifier for eifecting said opening of said switch to deenergize the electric power means.

3. In a signal seeking receiver, in combination, signal circuit tuning means including a frequency converter, means for amplifying the output of said converter at superaudible frequencies, electrical power means for varying said signal circuit tuning means, a normally closed switch controlling said power means, and means for opening said switch to de-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a balanced type of frequency discriminator-rectifier supplied by the output from said superaudible frequency amplifying means, and a control tube responsive to the output of said frequency discriminator-rectifier as the incoming signal frequency enters the frequency response spectrum'of the frequency discriminator-rectifier for effecting said opening of said switch to deenergize the electricpower means.

4; The'combination claimed in claim 3 in which said frequency discriminator-rectifier is fixed tuned to the frequency of said super audible amplifying means.

5. In a signal seeking receiver, in combination, signal circuit tuning means including a frequency converter, means for amplifying the output of said converter at superaudible frequencies, electrical power means for varying said signal circuit tuning means, a normally closed switch control-.- ling said power means, and means for opening said switch to de-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a signal amplitude limiter actuated by the output of said superaudible frequency amplifier, a balanced type of frequency discriminator-rectifier supplied by the output: of said amplifier, and a control tube responsive to the output of said frequency dis criminator-rectifier as the incoming signalfrequency enters the frequency response spectrum of the frequency discriminator-rectifier for effecting said opening of said switch to d'eenergize the electric power means.

6. In a signal seeking receiver, in combination, signal circuit tuning means including a frequency converter, means for amplifying the output of said converter at superaudible frequencies, said means having a band width suficiently wide to pass voice and music modulated signals of usual radio quality, a signal circuit tuning instrumentality, electrical power means for varying said 7 signal circuit tuning instrumentality, and means last-mentioned means comprising a balanced type of frequency discriminator-rectifier supplied by the output from said superaudible frequency amplifying means, and having a band width substantially less than said amplifying means, and a control tube responsive to the output of said discriminator for tie-energizing the electric power means.

'7. The combination claimed in claim 6, in which said frequency discriminator-rectifier is fixed tuned to the frequency of said superaudible amplifying means.

8. The combination claimed in claim 6, in which said frequency discriminator-rectifier has a frequency admittance band width a small fraction of that of said superaudible frequency amplifying means.

9. In a signal seeking receiver, in combination, signal circuit tuning means including a frequency converter, means for amplifying the output of said converter at superaudible frequencies, said means having a band width sufficiently wide to pass voice and music modulated signals of usual radio quality, a signal circuit tuning instrumentality, electrical power means for varying said tuning instrumentality, and means for de-energizing said electrical power means to stop the variation of said signal circuit tuning instrumentality in response to reception of an incoming signal of predetermined strength, said lastmentioned means comprising a signal amplitude limiter actuated by the output of said superaudible frequency amplifier, a balanced type of frequency discriminator-rectifier supplied by the output of said limiter and having an output substantially less than the band width of said amplifying means, and a control tube responsive to the output of said frequency discriminatorrectifier for de-energizing the electric power means.

10. In a signal seeking receiver, in combination, signal circuit tuning means, electrical power means for varying said signal circuit tuning means, a normally closed switch for controlling said power means, and means fer opening said switch to de-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a detector substantially balanced for impulses having substantially uniform energ distribution over its frequency admittance spectrum, but unbalanced to frequency variation, and a control tube responsive to the output of said detector for effecting said opening of said switch to deenergize the electric power means as the incoming signal frequency means, a normally closed switch for controlling said power means, and means for opening said switch to de-energize said electrical power means to stop the variation of said signal circuit tuning means in response to initial reception of an incoming signal of predetermined strength, said last-mentioned means comprising a signal amplitude limiter actuated by incoming signals, a detector substantially balanced for impulses having substantially uniform energy distribution over its frequency admittance spectrum, but unbalanced to frequency variation supplied by the output of said limiter, and a control tube responsive to the output of said detector for effecting said opening of said switch to deenergize the electric power means as the incoming signal frequency enters the frequency admittance spectrum of said detector.

MADISON G. NICHOLSON, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,152,336 Van Loon Mar. 28, 1939 2,182,352 Prochnow Dec. 5, 1939 2,207,467 Muller July 9, 1940 2,369,542 Dietrich Feb. 13, 1945 

